Cecil Frank Powell
British physicist and winner of the Nobel Prize for Physics in 1950
for his development of the photographic method of studying nuclear processes
and for the resulting discovery of the pion (pi-meson), a heavy subatomic
particle. The pion proved to be the hypothetical particle proposed in
1935 by Yukawa Hideki of Japan in his theory of nuclear physics.
In 1928 Powell was appointed research assistant at the Henry Herbert
Wills Physical Laboratory at the University of Bristol. He became professor
of physics at Bristol in 1948 and director of the Wills Laboratory in
1964. Between 1939 and 1945 he developed the necessary techniques for
using sensitive photographic emulsions to record the paths of cosmic
rays. In plates exposed at the top of high mountains or sent up in high-altitude
balloons, cosmic-ray interactions were recorded, and, in 1947, the data
revealed the existence of the pion ( +) as well as the process whereby
it decays into two other particles, an antimuon (mu-meson) and a neutrino.
Powell also discovered the antipion ( -) and, in 1949, the modes of
decay of kaons (K-mesons).